This invention relates to circuit simulators used in computer aided design of electronic circuits and systems. More particularly, this invention relates to simulator systems having the capability of simulating both analog and digital circuits.
There are many existing systems which provide the electrical engineer with circuit or system analysis capability. For example, the SPICE (Simulation Program with Integrated Circuit Emphasis, University of California at Berkeley) program has for many years provided analog signal analysis capability. Data concerning the circuit to be analyzed was generally provided to the computer by using conventional loop, node and component value data. Formatting such data is a slow and error prone task. Further, since a complete circuit analysis for every loop and node is provided, a large amount of time is required to run the program for circuits of some complexity.
More recently, such systems have been interfaced to high resolution graphics displays which permit schematic capture; that is, recording a circuit diagram as it is drawn and associating information about how the components of the circuit are connected and the function of the components with the finished "drawing" on the display.
There are also existing systems which model the operation of arrangements of digital circuits, thus permitting the engineer to simulate and therefore predict their operation without having to breadboard them. In addition, various methods and systems have been developed to test the operation of such circuits. An example of a digital analysis program is Mentor Graphics SIM.TM. or QUICKSIM.TM..
Some attempts have been made to perform analysis on circuits or systems having both analog and digital components. Such systems have generally proved to be unsatisfactory. By attempting to incorporate the best features of both analog and digital simulators, by compromising on speed and accuracy, these systems generally produce less than satisfactory results. A mixed analysis mode, which cannot be characterized as being analog or digital in nature, is used. Generally, only transient analysis of digital circuits with MOS transistors is possible. The only primitives supported are MOS transistors, resistors, capacitors and voltage sources referenced to ground. In contrast, SPICE supports sixteen primitives.
The engineering workstation (EW) has made available to the electrical engineer analog analysis programs, digital analysis programs, schematic capture routines, and high resolution graphics including multi-window displays. An example of such a system is that supplied by Mentor Graphics Corporation of Beaverton, Oregon. This workstation utilizes an Apollo Computers, Inc. Apollo.TM. computer and is programmed with Mentor Graphics MSPICE.TM. and QUICKSIM.TM. software. However, it does not have the capability of providing complete end-to-end simulation and analysis of circuits or systems having both analog and digital portions.